The Book of Ruth is the Book of Personal Redemption. The God of Creation, Who redeemed His chosen nation, and established a law for them to live under, and Who led them in the Conquest of the land, doesn’t just deal with nations and empires. He is a personal God, Who deals with each person on an individual basis.
Like Job, the Book of Ruth is named after it’s principle character. The Septuagint and the Hebrew Bibles are also named Ruth, in Greek and Hebrew.
The Book of Ruth does not declare who the author is, nor is the author of Ruth indicated in any other Book of the Bible. The Talmud attributes it to Samuel. As the historical bridge from Judges to 1st Samuel, that may be the most likely guess.